Feedback control system for marine propulsion engine

ABSTRACT

A number of embodiments of feedback control systems for maintaining the desired air fuel ratio in a marine propulsion engine that has an exhaust system for exhausting the exhaust gases to the atmosphere through an underwater exhaust gas discharge and wherein the discharge is adjustable relative to the associated watercraft. Conditions which will change the back pressure in the exhaust system are measured and the amount of fuel air ratio supplied to the engine by a feedback control system is varied, depending upon the sensed airflow and the sensed condition of the exhaust outlet that may affect back pressure and, accordingly, the ideal air fuel ratio. Spark ignition timing is also changed and the air fuel ratio may be corrected depending upon exhaust back pressure.

BACKGROUND OF THE INVENTION

This invention relates to an engine control system and method and moreparticularly to an improved feedback control system and method for amarine propulsion engine.

The control of an engine is extremely important in ensuring goodrunning. In addition to providing the appropriate and desired output forthe engine under a wide variety of running conditions, engine controlare important in ensuring good fuel economy and also effective exhaustemission control. Therefore, it has been proposed to provide engineswith sensors which sense the actual air-fuel ratio of the engine andmake adjustments through a feedback control system so as to ensure thatthe air-fuel ratio is obtained at the desired amount.

Although this theory may be relatively simple, the application of thisprinciple is not quite as straightforward. The problem is particularlyacute in conjunction with marine propulsion engines. Unlike landvehicles, the exhaust gases from a marine propulsion engine arefrequently discharged, under at least some running conditions, below thelevel of water in which the associated watercraft is operating. Thisunderwater exhaust gas discharge is employed so as to assist in exhaustsilencing.

With land vehicles the condition at the exhaust discharge generally ismaintained fairly constant under all running conditions. That is, thereare not outside factors which will affect the ability of the exhaustsystem to discharge the exhaust gases under most normal conditions.However, when the exhaust gases are discharged beneath the water, aswith a marine propulsion engine, then the condition at the exhaustoutlet can vary significantly.

One way in which the condition can vary is that the depth of theunderwater exhaust gas discharge is not constant during the running ofthe watercraft that is powered by the engine. In fact, the variationsare not even linear in relation to speed. The reason for this is thatmany watercraft use so-called "planing-type" hulls that operate fairlydeeply submerged under low-speed conditions. However, as the speedincreases and the watercraft goes on plane, the water level can changesuddenly relative to the location of the exhaust gas outlet. This canhave a significant effect on the performance.

It is, therefore, a principal object of this invention to provide animproved feedback control for a marine propulsion engine that takes intoaccount the pressure at the exhaust gas discharge.

It is a further object of this invention to provide an improved feedbackcontrol for a marine propulsion engine wherein the depth of submersionof the exhaust outlet is factored into the feedback control variables.

In addition to the depth of the exhaust outlet in marine applications,the exhaust gases are frequently discharged, particularly underhigh-speed operation, through a through- the-propeller orthrough-the-hub exhaust gas discharge. However, when the watercraft ispropelled by a propeller, it is the normal practice to mount thepropeller so that its trim position can be adjusted. That is, the angleof axis of rotation of the propeller relative to the transom is varied.This is done both in outboard motors and in the outboard drive portionof an inboard/outboard drive. These types of drives are referred togenerally as marine outboard drives.

In addition to changing the depth of submersion, the trim adjustmentchanges the angle at which the exhaust gases are discharged relative tothe water level. Hence, the back pressure on the exhaust gases can varywith the trim angle, even if the depth is maintained uniform.

It is, therefore, a still further object of this invention to provide animproved feedback control for a marine propulsion engine wherein thetrim angle of the drive is considered in setting the feedback control.

The types of feedback control employed generally control the air-fuelmixture by controlling the amount of fuel in response to the output ofthe sensor. The sensor is frequently an exhaust sensor, such as an O₂sensor, that emits a signal which is indicative of the richness orleanness of the mixture. If the feedback control is done only as afunction of the output of this sensor, the control may not be aseffective because it disregards the other factors noted above.

It is, therefore, a still further object of this invention to provide animproved feedback control system and method for a marine propulsionengine that takes into account exhaust back pressure and other factorswhich may affect it.

It has also been discovered that merely changing the amount of fuelsupplied to the engine does not necessarily achieve the complete resultsdesired. For example, with spark-ignited engines it has been found thatthe spark advance should also be altered in response to the feedbacksignal. Like the fuel-ratio variation, spark advance control alsodepends upon factors of exhaust gas pressure and other things that mayaffect it.

It is, therefore, a still further object of this invention to provide animproved feedback control system for the spark timing which is dependentupon factors affecting exhaust back pressure.

In controlling the air-fuel ratio, it is necessary, of course, toprovide a good indication of air flow to the engine so that the fuelflow that is varied can be varied in proportion to air flow. Withtwo-cycle engines, a type of engine frequently employed in marinepropulsion applications, it has been noted that the amount of air flowto the engine can be accurately determined by measuring the pressure inthe crankcase chamber at particular crank angles. Therefore, many enginecontrol systems employ crankcase pressure sensors so as to control theamount of fuel supplied.

It has been discovered, however, that the exhaust back pressure also canvary the accuracy of the crankcase pressure sensor in determining theaccurate airflow to the engine.

It is, therefore, a still further object of this invention to provide animproved feedback control system where the airflow is measured bycrankcase pressure and wherein adjustments are made in the air flowdetermination based upon factors which affect the back pressure in theexhaust system.

In engines that have plural cylinders, frequently the engine is suppliedwith an exhaust system that includes a manifold that collects exhaustgases from a number of exhaust ports and delivers it to the atmospherethrough a common exhaust gas opening of the exhaust system. With thesesystems and with particular applications the distance between theexhaust gas opening and the exhaust ports of the individual cylindersmay be different. This is a problem that is particularly acute inconjunction with marine propulsion applications due to the compactnature of the exhaust system that must be employed for theseapplications. This difference in length can be particularly significantin conjunction with two-cycle engines, wherein exhaust pulses can have asignificant effect on the charging of the individual cylinders. This iscaused in part by the substantial overlap between the opening of thescavenger port and the closing of the exhaust port. When utilizing afeedback control, the collected flow of the exhaust gases is normallymeasured, and this is used for determining the air-fuel ratio. As aresult, although the average for the system may be acceptable,individual cylinders are not supplied with the appropriate air-fuelmixture.

It is, therefore, a still further object of this invention to provide animproved feedback control system for an engine having plural cylindersserved by a common exhaust system and wherein the feedback control isvaried on a cylinder-by-cylinder basis.

It is frequently the practice to use a common basic engine architecturefor a family of engines. The engines within the family provide differentpower outputs or different performance, by varying the accessories andcomponents associated with the engine. Although this has advantages, italso has disadvantages. For example, it is necessary for themanufacturer, distributors, and dealers to stock a wide variety of partsto serve different engines of a common family. In addition, it makes itdifficult to judge and meet consumer preferences for varying desires.That is, more engines of one particular type may be desired in one yearthan in another year.

It is, therefore, a still further object of this invention to provide acontrol system for an engine wherein the basic structure of the engineis the same and its performance is varied only by the control strategyemployed so as to provide a family of engines which is substantiallyidentical in structure.

SUMMARY OF THE INVENTION

A first feature of the invention is adapted to be embodied in a fuelcontrol method and apparatus for a marine propulsion internal combustionengine. The engine is provided with a fuel supply device for supplyingfuel to the engine for combustion. The engine has an exhaust port fordischarging combustion products therefrom. An exhaust system collectsthe exhaust gasses from the engine and discharges them to the atmosphereat least in part below the level of water in which the propelled vesselis operating at least under certain running conditions. A sensor isprovided for sensing the air-fuel ratio supplied to the engine by thefuel supply device.

In accordance with a method for practicing this invention, the fuel issupplied to the engine by the fuel supply device. The output of thesensor is employed for adjusting the amount of fuel supplied to theengine in response to the output of the sensor to maintain the desiredair-fuel ratio. Means are provided for sensing a condition which willeffect the back pressure in the exhaust system, and the amount of fuelsupplied is adjusted in response to the sensed condition that willeffect the back pressure.

A method of practicing the invention comprises the steps of applyingfuel to the engine by the fuel supply device. The output of the sensoris read, and the amount of fuel supplied to the engine is varied inresponse to the output of the sensor to maintain the desired air-fuelratio. A condition which will effect the back pressure in the exhaustsystem is also sensed and the amount of fuel supplied is adjusted inresponse to this sensed condition.

Another feature of the invention is adapted to be embodied in a fuelcontrol method and apparatus for a two-cycle crankcase compressionmarine propulsion engine having a crankcase chamber containing acrankshaft. A fuel supply device is provided for supplying fuel to theengine for combustion. A crankcase pressure sensor senses the pressurein the crankcase chamber. The engine has an exhaust port from whichexhaust products are discharged. An exhaust system collects the exhaustgases from the engine exhaust port and discharges them to the atmosphereat least in part below the level of water in which the propelled vesselis traveling-under at least certain running conditions. In accordancewith an apparatus for practicing this facet of the invention, thecrankcase pressure is measured at a predetermined crankshaft angle so asto provide an indication of air flow for controlling the amount of fuelsupplied by the fuel supply device. A further sensor is provided forsensing a condition which will effect exhaust gas pressure, and theairflow calculation is corrected depending upon the sensed condition.

In accordance with a method for practicing this facet of the invention,the amount of air flowing to the engine is determined by measuring thecrankcase pressure at a predetermined crankshaft angle. In addition, acondition is sensed which will effect exhaust gas back pressure, and theamount of fuel supplied to the engine is varied in response to thecomputed air flow and the back pressure condition.

A further feature of the invention is adapted to be embodied in anapparatus and method for an internal combustion engine having aplurality of cylinders. A fuel supply device is provided for supplyingfuel to the engine for combustion. A plurality of exhaust ports in theengine discharge combustion products from the individual cylindersthereof. An exhaust system collects the exhaust gases from the engineexhaust ports and discharges them to the atmosphere through a commonexhaust opening. A sensor senses the air-fuel ratio supplied to theengine by the fuel supply device.

An apparatus for controlling the engine includes means for controllingthe amount of fuel supplied to the engine by the charge-forming systemin response to the output of the sensor. The amount of fuel supplied tothe engine is varied in response to the output of the sensor to maintainthe desired air-fuel ratio, but the amount of fuel supplied to eachcylinder is varied, dependent upon the distance of that cylinder'sexhaust port from the exhaust outlet so as to maintain the appropriateair-fuel ratio in each cylinder.

A method for practicing this invention comprises the steps of adjustingthe amount of fuel supplied to the engine in response to the output ofthe sensor. The amount of fuel supplied to each cylinder is varied,dependent upon its distance from the exhaust outlet so as to compensatefor these differences and maintain the desired air-fuel ratio for eachcylinder.

Another feature of the invention is adapted to be embodied in a methodfor operating engines and an engine that can be used for a variety ofapplications requiring different outputs of the engine. The engineincludes a number of cylinders, a fuel supply system for supplying fuelto the cylinders, and an ignition system for firing the charge in thecylinders.

In accordance with an apparatus for practicing the invention, thespecific output of the engine is varied to provide the desiredperformance by changing the control strategy of at least one of the fuelsupply system and the ignition system.

In accordance with a method for practicing the invention, the differentoutputs required from the engine are achieved for the respectiveapplications by varying one of the fuel control and ignition systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic view of an outboard motor constructedand operated in accordance with an embodiment of the invention, with theoutboard motor being shown in side elevation, in a vertical crosssection, and schematically in a horizontal cross section so as to showthe interrelationship of all of the components.

FIG. 2 is a graph showing the air-fuel ratio corrections relative toexhaust gas back pressure, with the target air-fuel ratio being shown bythe broken line and the corrective amount required indicated.

FIG. 3 is a graphical view showing the spark timing correction inresponse to exhaust gas pressure, with the standard initial value andthe corrective amounts to accommodate back pressure being shown.

FIG. 4 is a view showing the map of fuel injection amount in response toair flow, as determined by crankcase pressure at a particular crankangle, and engine speed.

FIG. 5 is a graph showing the corrective amount of fuel injection inresponse to the same parameters as FIG. 5, i.e., air flow and enginespeed.

FIG. 6 is a block diagram showing the relationship of the oxygen sensor,feedback control, and fuel injector.

FIG. 7 is a block diagram showing how the map values of FIGS. 4 and 5are combined to output a signal to the controller for controlling thefuel injector in response to sensed engine conditions and correctivefactors based upon exhaust gas back pressure.

FIG. 8 is a graphical view showing the output signal of the oxygensensor and the resulting feedback control routine in relation to time.

FIG. 9 ms a graphical view showing the exhaust back pressure under threeoperating conditions of the outboard motor: idle, forward trolling, andreverse trolling.

FIG. 10 is a graphical view showing the torque curves at idle andtrolling with various mixture strengths, with stoichiometric conditionsbeing shown in the solid vertical line 80=1

FIG. 11 is a view, in part similar to FIG. 8, but shows the feedbackcontrol conditions and oxygen sensor conditions at idle, as shown in thedotted-line view, and when trolling, as shown in the solid-line view.

FIG. 12 is a block diagram showing the relationship of the backpressure, trim angle, and crankcase pressure sensors to the controllerand how the fuel injection and spark timing are controlled in responseto these signals.

FIG. 13 is a graphical view showing the relationship of trim angle toexhaust gas back pressure.

FIG. 14 is a graphical view showing how crankcase pressure varies asexhaust gas back pressure varies.

FIG. 15 is a graphical view showing how crankcase pressure varies duringa portion of the rotation of the crankshaft.

FIG. 16 is a graphical view showing how the air-fuel ratio in eachcylinder varies in relation to engine speed when the mixture strength isset to be the same due to differences in distance between the end of theexhaust gas opening and the exhaust port of the respective cylinders.

FIG. 17 is a graphical view showing how the spark advance angle shouldbe varied with engine speed for each cylinder to compensate for thefactors mentioned in conjunction with FIG. 16.

FIG. 18 is a graphical view showing how the fuel injection amount foreach cylinder should be varied with engine speed so as to maintain thedesired air-fuel ratio for each cylinder to compensate for the factorsnoted.

FIG. 19 is a graphical view showing how spark advance for each cylindershould be corrected in response to engine speed.

FIG. 20 is a graphical view showing a timing diagram showing the sparkadvance control range and the position for maximum power spark advancetiming to illustrate how the performance of the engine can be varied bymerely altering the control routine.

FIG. 21 is a graphical view showing the fuel injection initiation timingin response to crankshaft angle in order to permit variation in engineoutput by controlling this parameter.

FIG. 22 a timing diagram showing how fuel injection duration can bevaried through varied engine output in accordance with the invention atmaximum power.

FIG. 23 is a graphical view showing power and brake specific fuelconsumption in relation to engine speed with the various controlroutines to obtain different performances from the same engine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Referring now in detail to the drawings and initially to FIG. 1, anoutboard motor is identified generally by the reference numeral 11. Thisview is composite view showing the complete outboard motor 11 in sideelevation in a fully trimmed down position, in a vertical cross sectionabout a plane perpendicular to the side elevation and schematically witha single cylinder of the powering internal combustion engine is shown incross section. The engine is identified generally by the referencenumeral 12 and the associated fuel injection system for it shownpartially in cross section and partially schematically.

The invention is described in conjunction with an outboard motor only asa typical environment in which the invention may be practiced. Theinvention has particular utility with two cycle crankcase compressioninternal combustion engines and since such engines are frequentlyemployed as the power plants for outboard motors, an outboard motor is atypical environment in which the invention may be employed. Theinvention also has particular utility in conjunction with the use ofengines for powering watercraft wherein at least a portion of theexhaust gases are delivered through an underwater exhaust gas discharge.This type of exhaust system is utilized with either outboard motors orwith the stern drive portion of inboard/outboard drives, as has alreadybeen noted.

The outboard motor 11, as already noted, includes a powering internalcombustion engine 12 which, in the illustrated embodiment, is comprisedof a three cylinder in-line engine. It will be readily apparent to thoseskilled in the art how the invention can be employed in conjunction withengines of other configurations.

The engine 12 forms a portion of the power head of the outboard motorand this power head is completed by a protective cowling 13 whichsurrounds the engine 12 in a known manner. As may be seen in the lowerleft hand view of this figure, the engine 12 is comprised of a cylinderblock 14 in which three aligned cylinder bores 15 are formed. Pistons 16reciprocate in the cylinder bores 15 and are connected to connectingrods 17 which, in turn, drive a crankshaft 18 in a well known manner.The crankshaft 18 is rotatably journaled within a crankcase assemblywhich is divided into individual chambers 19 each associated with arespective one of the cylinder bores 15 and which are sealed from eachother in a manner well known in this art.

A fuel/air charge is delivered to the crankcase chambers 19 by aninduction system, indicated generally by the reference numeral 21, andwhich includes an atmospheric air inlet 22 in which a manually operatedthrottle valve 23 is positioned. Electronically operated fuel injectors24 spray fuel into an intake manifold 25 downstream of the throttlevalve 23. The fuel injectors 24 receives fuel from a fuel systemincluding a remotely positioned fuel tank 26. Fuel is drawn from thefuel tank 26 by means of a high pressure fuel pump 27, through a conduit28 in which a filter 29 is positioned. This fuel then delivered to afuel rail 31 in which a pressure regulator 32 is provided. The pressureregulator 32 maintains the desired pressure in the fuel rail bybypassing excess fuel back to the fuel tank 26 through a return conduit33. The operation of the fuel injector 24 will be described in moredetail later.

The intake manifold 25 delivers air to the intake ports 34 of the enginethrough reed type check valves 35 which operate to preclude reverseflow. The inducted charge is drawn into the crankcase chambers 19 uponupward movement of the pistons 16 and then is compressed upon downwardmovement. The compressed charge is then transferred to the area abovethe pistons 16 through a plurality of scavenge passages 36 in a mannerwell known in this art.

A cylinder head 37 is affixed to the cylinder block 14 in a known mannerand defines a recess which forms part of the combustion chamber. A sparkplug 38 is mounted in each cylinder recess and is fired by the ignitionsystem in a known manner.

The cylinder block 14 is formed with an exhaust port 39 for eachcylinder which communicates with an exhaust manifold 41 formed in partin the cylinder block 14.

As is typical with outboard motor practice, the cylinder block 14 andcylinder head 37 are formed with cooling jackets through which coolantis circulated from the body of water in which the outboard motor 11 isoperating in any conventional manner.

A driveshaft housing 42 depends from the power head and rotatablyjournals a driveshaft which is driven by the engine crankshaft 18 in aknown manner. The driveshaft housing 42 is formed with an internalexpansion chamber 43 to which exhaust gases are delivered from theexhaust manifold 41 by an exhaust pipe 44. Any suitable internalbaffling and cooling system is provided for the exhaust gases and theyare then discharged through a conventional underwater high speed exhaustgas discharge, which may comprise an outlet formed in the lower unit 45or in the hub of a propeller driven by the driveshaft. In addition, anabove the water, low speed gas discharge may be incorporated.

As is typical with outboard motor practice, a steering shaft (not shown)is connected to the driveshaft housing 42 in a known manner. Thissteering shaft is journaled for steering movement about a generallyvertically extending steering axis within a swivel bracket 46. Theswivel bracket 46 is, in turn, pivotally connected to a clamping bracket47 for tilt and trim movement about a horizontally disposed axis by apivot pin 48. The lower right hand side view of FIG. 1 shows theoutboard motor 11 in a fully trimmed down position where it is disposedat the angle β to the transom of the associated watercraft. The trim maybe adjusted in any known manner.

In addition, the pivotal connection 48 permits the outboard motor 11 tobe tilted up out of the water when not in use. For control purposes, aswill be described, a trim position indicator 49 is mounted to cooperatebetween the clamping bracket 47 and swivel bracket 46 to provide anoutput signal to an ECU, indicated generally the reference numeral 51.The total control strategy will be described later.

The construction of the outboard motor 11 and its powering internalcombustion engine 12 as thus far described may be considered to beconventional and all of the components which have been illustrated maybe of any conventional type. Since the invention deals with the fuelinjection and spark control systems for the engine and their control, itis believed unnecessary to describe in further detail the components ofthe engine which may be considered to be conventional.

Referring now in more detail to the fuel injection system and thecontrol therefor, as previously noted, the fuel injectors 24 areelectronically controlled. To this end, it is provided with anelectrical terminal 52 that receives an output control signal from theECU, through a conductor indicated the line 53. A solenoid of the fuelinjectors 24 is energized when the ECU 51 outputs a signal to theterminal 51 through the line 53 to open an injection valve and initiateinjection. Once this signal is terminated, injection will also beterminated. The injectors 24 may be of any known type and in addition toa pure fuel injectors may comprise an air/fuel injectors.

A number of ambient atmospheric conditions are supplied to the ECU 51and certain engine running conditions are supplied to the ECU 51 so asto determine the amount of fuel injected and the timing of the fuelinjection. These ambient conditions may comprise atmospheric pressurewhich is measured in any suitable manner by a sensor and which signal istransmitted to the ECU 51 through a conductor 60, temperature of theintake cooling water which is delivered to the engine cooling jacketfrom the body of water in which the watercraft is operating as sensed byan appropriate sensor (not shown) and transmitted through to the ECU 51through a conductor 56, and the intake air temperature is sensed in thecrankcase chamber 19 by a temperature sensor 57 which outputs its signalto the ECU 51 through a conductor 58. Additional ambient conditions maybe measured and employed so as to provide more accurate control of thefuel injection, if desired.

There are also provided a number of engine condition sensors which sensethe following engine conditions. An in-cylinder pressure sensor 59senses the pressure within the cylinder and outputs this signal to theECU 51 through a conductor 61. A throttle valve position sensor 62senses the position of the throttle valve 23 and outputs this signal tothe ECU 51 through a conductor 63. Crankcase pressure is sensed by apressure sensor 64 which is also mounted in the crankcase chamber 19 andoutputs its signal to the ECU 52 through a conductor 65. Crank angleposition indicative of the angular position and rotating speed of thecrankshaft 18 is determined by a sensor 66 and outputted to the ECU 51through a conductor 67. Engine temperature is sensed by a sensor 68mounted in the cylinder block 14 and inputted to the ECU 51 through aconductor 69. Exhaust system back pressure in the expansion chamber 43is sensed by a sensor 71 and is outputted to the ECU 54 through aconductor 72. Finally, a knock sensor (not shown) output a signal to theECU 51 when a knocking condition is sensed through the conductor 73. Aswith the ambient conditions, additional engine running conditions may besensed. Those skilled in the art can readily determine how such otherambient or running conditions can be sensed and fed to the ECU 51 andprocessed by the ECU 51 to determine the fuel injection supply both intiming and amount.

As is disclosed in U.S. Pat. No. 4,461,260 entitled "Fuel InjectionSystem For Two-Cycle Internal Combustion Engines," issued Jul. 24, 1984,the airflow to the engine can be accurately measured by the crankcasepressure sensor 64 when the pressure reading is taken at a specificcrankshaft angle as set forth therein. However, as will be discussedbelow, it has been discovered that the back pressure in the exhaustsystem as sensed by the sensor 71 will effect the accuracy of thecrankcase pressure in indicating air flow. As will be described later, acorrection is made for this condition as well as trim angle condition assensed by the sensor 49.

A transmission condition sensor (Not Shown) for the transmission in thelower unit also sends a transmission position (F, N or R) to the ECU 51through a conductor 54.

Finally, the engine control and particularly the air fuel ratio iscontrolled by controlling the timing of the beginning of injection bythe fuel injectors 24 and the duration of injection through a feedbackcontrol system. This system includes an oxygen sensor 74 that is placedin a bypass passage 75 that interconnects the exhaust passages from twoadjacent cylinders and is located in a location wherein it will be leasteffected by exhaust system back pressure.

The ECU 51 is programmed to provide a feedback control system based uponthe output of the oxygen sensor 74 and any other engine factors in aconventional manner. However, in accordance with an important feature ofthe invention, this feedback control is modified based upon certainfactors which will tend to cause the output from the oxygen sensor 74not to be truly indicative of the actual conditions that determine theappropriate air fuel ratio. Generally the system is designed to maintaina stoichiometric mixture where actual air fuel ratio divided bystoichiometric is equal to 1 (80=1), but it has been found that thedesirable feedback control of the fuel mixture and the spark advance arealso effected by actual exhaust system back pressure as sensed by thesensor 71.

This may be understood by reference to FIG. 2, which is a graphical viewshowing air fuel ratio in relation to exhaust back pressure. Shown onthis graph is standard of initial value at idle condition. It will beseen that if the exhaust gas pressure falls below normal, the exhaustgases can flow more freely and the air flow into the cylinder will begreater so that the mixture tends to become lean. Therefore, if theexhaust back pressure falls below the initial value, then the systemshould add to the fuel supplied so as to compensate for its leanness.

On the other hand, if the back pressure raises, then the flow of exhaustgases is retarded and the air intake amount is decreased and the mixturetends to become rich. Therefore, the system leans the fuel from whatwould normally be provided under this condition in order to maintainstoichiometric conditions. It should be noted that in this descriptionit is assumed that the desired air fuel ratio is stoichiometric.However, where this term is used, it is to understood that it couldequally be the desired air fuel ratio which might be on the lean or richside, depending upon the particular engine design.

In a similar manner and as shown in FIG. 3, the ideal spark timing alsois dependent upon exhaust back pressure. If the pressure falls below thenormal or designed value, then the spark should be retarded becauseflame will tend to propagate faster and this is done so as to avoid thepeak pressure occurring at the incorrect time. On the other hand, ifback pressure rises, then the flame will propagate slower and the sparkshould be advanced.

The strategy by which the system operates will now be described byreference to FIGS. 4-6. FIG. 4 is a map which is pre-programmed into theECU 51 and shows the amount of fuel that should be supplied for variousinduction system air flows and engine speeds. As has been previouslynoted, the air flow to the engine is calculated in accordance with thedescribed embodiment by taking the pressure in the crankcase chamberfrom the pressure sensor 64 at a specific crank angle.

FIG. 5 is a graph showing the corrective factors in relation to enginespeed and air flow from data that is obtained by actually measuring thesituation with various back pressures that will exist under theseconditions and other variable which may be employed such as transmissioncondition for the corrective factor. As may be seen in FIG. 6, theoutput from the oxygen sensor 74 is supplied to the feedback controlsystem, which is identified by the reference numeral 76 in this figure,which, in turn, outputs its signal to the terminal 52 of the fuelinjector 24 so as to control both the timing and duration of fuelinjection. These features will be described later by reference toanother embodiment wherein the performance of the engine 12 can bevaried by changing fuel injection timing, duration and spark timing.

FIG. 7 is a graphical view showing how the actual correction is made inthe ECUs 51. The ideal fuel amount for the engine running condition isread at the section 77 from the map of FIG. 4. At the same time orsubsequently, the corrective amount of fuel is read at the section 78from the map of FIG. 5. These values are then transmitted to a summingcalculator section 79 which sums the values and outputs a signal to acontroller 81 which then outputs its signal to the fuel injector 24 soas to inject the appropriate amount of fuel.

FIG. 8 is a graphical view showing how the feedback control is obtainedwith the feedback control system. The top portion of the graph shows theoutput of the oxygen sensor while the bottom portion shows theadjustments being made to vary the fuel air ratio from stoichiometric,indicated at 1. The oxygen sensor depicted is of the type which outputsa voltage signal which is between 0 and 1 volts. The condition atapproximately 500 millivolts is indicative that the mixture has gonerich.

Starting at the left hand side of this graph, it will be seen that themixture has been lean and accordingly the feedback control has beenenriching the mixture in steps. However, at the point when the oxygensensor outputs its signal, then the feedback control begins a leaningprogram by first creating a large reduction in the amount of fuel flowand then stepping the reduction down slowly until the oxygen sensor nolonger outputs its signal. Then the program repeats in an enrichingdirection making a large initial adjustment and then smaller adjustmentsuntil the oxygen sensor again outputs its signal.

The actual air fuel ratio to achieve stoichiometric also varies inresponse to the operating condition of the associated watercraft. FIG. 9shows how the back pressure varies under some typical running conditionsof a watercraft. It may be seen when the watercraft is stationary withthe engine idling (transmission in neutral) forwardly with the engine atidling (idling speed) that the back pressure is higher than whenoperating at trolling speed. As is well known, trolling speed is lowerthan actual idle speed because of the power required to propel the boatthrough the body of water. Also the operation of the propeller and themovement of the watercraft in a forward direction assists in the exit tothe exhaust gasses. On the other hand, when trolling in reverse, theback pressure goes up because of the fact that the direction of movementof the outlet of the exhaust discharge through the propeller is facingthe direction of water flow, and hence there will be some ram affectthat will restrict the flow of exhaust gases under this operationalmode. Thus the system in the ECU 51 is also responsive to transmissioncondition.

FIG. 10 is a view showing the torque curves at various air fuel ratioswhen operating at idle as shown in the broken line view and whentrolling as shown in the solid line view. As may be seen the range (a)when the engine has good combustion on the lean side is greater in trollthan in idle (a'). This is also due to the reduced back pressure. FIG.11 shows how the system compensates by changing the reference output ofthe oxygen sensor in response to the running conditions and illustratesthe settings under idle and troll and the feedback operations under eachsystem in order to maintain a stoichiometric condition regardless ofoperational mode of the watercraft so as to compensate for thevariations in back pressure caused by these various operational modes asalready noted.

In addition to the depth at which the exhaust is discharged and thespeed of travel of the watercraft or its operational mode affecting theideal air fuel ratio, the trim adjustment also has been found to affectthese conditions. FIG. 13 shows how the trim angle affects exhaustpressure. When fully trimmed down, the exhaust back pressure is at itshighest and the back pressure decreases, but not linearly as the driveis trimmed up.

Changing the trim not only changes the height of the exhaust outlet, butalso its angle to the water. When fully trimmed down, the exhaust gasesare directed totally at the water and have no significant componentdirected toward the air above the water. However, as the outboard driveis trimmed up, then the exhaust gas outlet through the hub propellerdischarge begins to face upwardly and the exhaust gases can exit moreeasily because they need travel less distance to reach the atmosphere,and hence the back pressure will decrease.

Thus, it is also possible to employ a section, shown at the block 82 ofthe ECU 51, that receives not only exhaust back pressure signal from thesensor 71 and crankcase pressure from the sensor 64, but also the outputof the trim sensor 49 so as to adjust not only the fuel injector 24 butalso the timing of firing of the spark plugs 38.

FIGS. 14 and 15 are graphical views that show how the exhaust backpressure effects the crankcase pressure if all other things areconstant. FIG. 15 is a graphical view and shows how the crankcasepressure varies during a cycle of operation reaching its maximum at thetime when the scavenge port opens and falls to a minimum intermediatevalue at the time S1 and P1 before the scavenge port closes. It,is thisvalue P1 that is measured in accordance with the aforenoted methoddescribed in U.S. Pat. No 4,461,260 that is employed to measure airflow.

FIG. 14 shows how the value of P1 varies with exhaust gas back pressure.If the back pressure is lower than normal, indicated by the point α, thecrankcase pressure will be lower while as the exhaust back pressureincreases the crankcase pressure will increase. Again, these functionsare not linear. This is another reason why exhaust back pressure must betaken into account to obtain ideal feedback control because the airflowcalculation which is based on the crankcase pressure will also varydependent upon exhaust back pressure.

In addition to the factors which have already been discussed, it hasalso been discovered that the ideal air fuel ratio for the engine 12varies cylinder by cylinder. Considering the number of cylinders as 1, 2and 3, beginning at the top, it is found that since the exhaust manifold41 which collects the exhaust gases from the exhaust port 39 must berelatively compact and, as is known, exhaust pulses are delivered backto the individual exhaust ports from the end of the exhaust pipe 44. Theeffect of this varies from cylinder to cylinder because of the fact thatthe exhaust ports 39 for each cylinder are disposed at differentdistance from the end of the exhaust pipe 44. The effect of this on bothair fuel ratio and ideal spark advance is shown in FIGS. 16 and 17 whichshows the air fuel ratio and ideal spark advance for each cylinder.Hence, in addition to the corrections already noted, the amount ofadjustment or correction for each cylinder must be different and the ECU51 also includes a map that provides the appropriate corrections toaccommodate this situation. These corrective values in fuel injectionamount and spark advance are shown in FIG. 18 and 19.

From the foregoing description, it should be readily apparent that thefeedback control system of the ECU 51 is highly effective in insuringthat the stoichiometric or desired air fuel ratio is maintained not onlyby the engine 12 but within each of its cylinders. Also, it is believedthat the foregoing description indicates the performance of the enginecan be varied significantly by changing spark timing, fuel injectionamount and fuel injection duration. This permits a single basic engineto be tuned by varying these factors to provide different power curvesand break specific fuel consumption curves as shown in FIG. 23. Byvarying these factors, the power and BSFC curves can be varied as shownin the areas a, b and c, with the effect being particularly noticeableat the high end of the power curve.

FIG. 20 is a crankshaft timing diagram showing the control range ofspark advance and how the maximum power can be changed within theacceptable range indicated in this figure so as to alter the engineperformance. FIG. 21 is a corresponding timing diagram showing how thestart of fuel injection can be employed to vary the power. This curveshows the point of beginning of fuel injection when maximum power can beachieved with is approximately at the time of scavenge port closing andan acceptable range within which the injection amount can be altered toreduce the power while, at the same time, providing generally goodengine performance.

FIG. 22 is a further view showing how the performance can be changedalso by changing the fuel injection duration. This shows a curve usingone of the injection timing starting points of FIG. 22 and shows how bychanging the stopping time within the control range from the optimumperformance point A, the performance can be varied. Thus, by employingthese variables it is possible to have engines of a range ofperformances available even though the basic engine is identical. Thischanged performance can be merely programmed into the ECU 51 to achievethese performance variations.

It should be readily apparent from the foregoing description that thedescribed embodiments are very effective in meeting the objects as setforth. Of course, various changes and modifications may be made withoutdeparting from the spirit and scope of the invention, as defined by theappended claims.

We claim:
 1. A fuel control method for a marine propulsion, internalcombustion engine comprised of a fuel supply device for supplying fuelto the engine for combustion, an exhaust port in the engine fordischarging combustion products therefrom, an exhaust system forcollecting exhaust gases from said engine exhaust port and having anexhaust outlet discharging said collected exhaust gases to theatmosphere at least in part below the level of water in which a vesselpropelled by said engine is traveling at least under certain runningconditions, and an air fuel ratio sensor for sensing an air fuel ratiosupplied to the engine by said fuel supply device, said methodcomprising the steps of supplying fuel from said fuel supply device tosaid engine, detecting and reading an output from said air fuel ratiosensor, adjusting an amount of fuel supplied to said engine by said fuelsupply device in response to said output of said air fuel ratio sensorto maintain a predetermined air fuel ratio, sensing a predeterminedcondition that will effect a back pressure in said exhaust system, andadjusting said fuel supplied from said fuel supply device in response tosaid sensed predetermined condition for compensating for variations infuel supplied to said engine due to said exhaust back pressure.
 2. Thefuel control method for a marine propulsion, internal combustion engineas set forth in claim 1, wherein the exhaust back pressure is alsosensed by a pressure sensor in the exhaust system.
 3. The fuel controlmethod for a marine propulsion, internal combustion engine as set forthin claim 1, wherein the exhaust outlet of the exhaust system isassociated with a propulsion device for propelling the vessel and meansare provided for changing the relation of the propulsion device andexhaust outlet relative to the vessel.
 4. The fuel control method for amarine propulsion, internal combustion engine as set forth in claim 3,wherein the condition sensed is the relative position of the exhaustoutlet and the propulsion device relative to the vessel.
 5. The fuelcontrol method for a marine propulsion, internal combustion engine asset forth in claim 4, wherein the relative position is determined by atrim sensor.
 6. The fuel control method for a marine propulsion,internal combustion engine as set forth in claim 5, wherein thepropulsion device and exhaust outlet are pivotally supported on thevessel and the sensing device senses the pivotal position.
 7. The fuelcontrol method for a marine propulsion, internal combustion engine asset forth in claim 1, wherein the engine is spark ignited and furtherincluding a spark control system for controlling the time at which thespark plug is fired.
 8. The fuel control method for a marine propulsion,internal combustion engine as set forth in claim 7, wherein the sparktiming is also adjusted in response to the sensed condition that effectsexhaust back pressure in the exhaust system.
 9. The fuel control methodfor a marine propulsion, internal combustion engine as set forth inclaim 8, wherein the exhaust back pressure is also sensed by a pressuresensor in the exhaust system.
 10. The fuel control method for a marinepropulsion, internal combustion engine as set forth in claim 8, whereinthe exhaust outlet of the exhaust system is associated with a propulsiondevice for propelling the vessel and means are provided for changing therelation of said propulsion device and said exhaust outlet relative tosaid vessel.
 11. The fuel control method for a marine propulsion,internal combustion engine as set forth in claim 10, wherein thecondition sensed is the relative position of the exhaust outlet and thepropulsion device relative to the vessel.
 12. The fuel control methodfor a marine propulsion, internal combustion engine as set forth inclaim 11, wherein the relative position is determined by a trim sensor.13. The fuel control method for a marine propulsion, internal combustionengine as set forth in claim 11, wherein the propulsion device andexhaust outlet are pivotally supported on the vessel and the sensingdevice senses the pivotal position.
 14. The fuel control method for amarine propulsion, internal combustion engine as set forth in claim 1,wherein the engine is a two-cycle, crankcase compression engine.
 15. Thefuel control method for a marine propulsion, internal combustion engineas set forth in claim 14, wherein the amount of fuel supplied by thefuel supply device is varied in response to air flow to the engine andwherein said air flow is determined by sensing the pressure in thecrankcase.
 16. The fuel control method for a marine propulsion, internalcombustion engine as set forth in claim 15, wherein the exhaust backpressure is sensed by a pressure sensor in the exhaust system.
 17. Thefuel control method for a marine propulsion, internal combustion engineas set forth in claim 15, wherein the exhaust outlet of the exhaustsystem is associated with a propulsion device for propelling the vesseland means are provided for changing the relation of said propulsiondevice and said exhaust outlet relative to said vessel.
 18. The fuelcontrol method for a marine propulsion, internal combustion engine asset forth in claim 17, wherein the condition sensed is the relativeposition of the exhaust outlet and the propulsion device relative to thevessel.
 19. The fuel control method for a marine propulsion, internalcombustion engine as set forth in claim 18, wherein the relativeposition is determined by a trim sensor.
 20. The fuel control method fora marine propulsion, internal combustion engine as set forth in claim19, wherein the propulsion device and exhaust outlet are pivotallysupported on the vessel and the sensing device senses the pivotalposition.
 21. The fuel control method for a marine propulsion, internalcombustion engine as set forth in claim 1, wherein the engine has aplurality of cylinders, each being served by a respective exhaust port.22. The fuel control method for a marine propulsion, internal combustionengine as set forth in claim 1, wherein the exhaust system comprises acollector section for collecting the exhaust gases from all of theexhaust ports and delivering them to the exhaust outlet, and whereineach of the exhaust ports is spaced at a distance from the exhaustoutlet different from the others.
 23. The fuel control method for amarine propulsion, internal combustion engine as set forth in claim 22,wherein the fuel supply device comprises a plurality of fuel supplydevices, each supplying fuel to a respective cylinder and wherein theamount of fuel supplied by each fuel supply device is varied dependingupon the distance of the exhaust port from the exhaust outlet.
 24. Thefuel control method for a marine propulsion, internal combustion engineas set forth in claim 22, wherein the exhaust back pressure is sensed bya pressure sensor in the exhaust system.
 25. The fuel control method fora marine propulsion, internal combustion engine as set forth in claim24, wherein the engine is spark ignited and further including a sparkcontrol system for controlling the time at which the spark plug isfired.
 26. The fuel control method for a marine propulsion, internalcombustion engine as set forth in claim 25, wherein the spark timing isalso adjusted in response to the sensed condition that effects the backpressure in the exhaust system.
 27. The fuel control method for a marinepropulsion, internal combustion engine as set forth in claim 26, whereinthe exhaust back pressure is sensed by a pressure sensor in the exhaustsystem.
 28. The fuel control method for a marine propulsion, internalcombustion engine as set forth in claim 27, wherein the exhaust outletof the exhaust system is associated with a propulsion device forpropelling the vessel and means are provided for changing the relationof the propulsion device and exhaust outlet relative to the vessel. 29.The fuel control method for a marine propulsion, internal combustionengine as set forth in claim 27, wherein the fuel supply devicecomprises a plurality of fuel supply devices, each supplying fuel to arespective cylinder and wherein the amount of fuel supplied by each ofsaid fuel supply device is varied depending upon the distance of theexhaust port from the exhaust outlet.